液相色谱-串联质谱法同时测定牛奶和奶粉中5种非蛋白含氮化合物

Simultaneous Determination of 5 Nitrogen-Rich Adulterants in Milk and Powdered Milk by LC-MS/MS

建立了液相色谱-串联质谱（LC-MS/MS）测定牛奶和奶粉中地昔尼尔、双氰胺、缩二脲、环丙氨嗪和三聚氰胺5种非蛋白含氮化合物的方法。样品经乙腈沉淀蛋白并提取,正己烷脱脂,HLB固相萃取柱净化,LC-MS/MS法检测,同位素稀释内标法或外标法定量分析。结果表明：地昔尼尔、双氰胺、缩二脲、环丙氨嗪和三聚氰胺在牛奶样品中的定量限（S/N=10）分别为0.5、2.5、20、5、15μg/kg,在奶粉样品中的定量限（S/N=10）分别为8、35、50、40、50μg/kg;方法的线性关系良好,线性相关系数R2大于0.991;回收率为72.4%～102.8%,相对标准偏差（RSD）为1.3%～12.3%。采用该方法检测55批次牛奶和奶粉样品中5种化合物的残留情况,其中阳性样品的测定结果与国家标准方法的测定结果一致,验证了方法的可靠性。该方法简便、快捷,定量限可满足目前国内外最大残留限量的要求,可作为乳制品中相关化合物残留量的测定方法。

A method of liquid chromatography-tandem mass spectrometry（LC-MS/MS）was developed for the determination of five nitrogen-rich adulterants（dicyclanil,dicyandiamide,biuret,cyromazine,melamine）in milk and powdered milk samples.These compounds were potential to be used in economic adulteration to enhance the nitrogen content in milk products.The protein of sample was precipitated,and the extracts were dissolved and distilled with acetonitrile.The supernatant solution wasextracted with n-hexane to remove the fat,and then cleaned up with SPE HLB cartridges.The quantitative detection was performed on LC-MS/MS by multiple reaction monitoring（MRM）mode under positive electrospray ionization（ESI＋）.Isotopes dilution internal standard method（melamine）or external standard method（dicyclanil,dicyandiamide,biuret and cyromazine）was used to determine the residue contents in samples.The limits of quantification（LOQs,S/N=10）are dicyclanil（0.5μg/kg）,dicyandiamide（2.5μg/kg）,biuret（20μg/kg）,cyromazine（5μg/kg）,melamine（15μg/kg）for milk samples and dicyclanil（8μg/kg）,dicyandiamide（35μg/kg）,biuret（50μg/kg）,cyromazine（40μg/kg）,melamine（50μg/kg）for powered milk samples.Single-laboratory method validation data are determined,the calibration standard curves concentration are 0,50,100,200,400μg/kg and the correlation coefficients are more than 0.991.The average recovery is 72.4%-102.8%,and the relative standard deviation（RSD）is 1.3%-12.3%.The residues of 5compounds in 55 batches of milk and milk powder samples are determined by LC-MS/MS,and the results are consistent with the national standard method（GB/T 22388—2008）.This method is suitable for determination and confirmation of these compounds and provides a convenient,rapid and effective approach to proactively combat economically motivated adulteration in milk and powdered milk sample.